1. Field of the Invention
The present invention relates to a power headroom calculation method and apparatus. More particularly, the present invention relates to a power headroom calculation method and apparatus of a User Equipment (UE) for a primary cell in a Long Term Evolution-Advanced (LTE-A) mobile communication system.
2. Description of the Related Art
Mobile communication systems have been developed to provide subscribers with voice communication services on the move. With the rapid advance of technologies, the mobile communication systems have evolved to support high speed data communication services as well as the standard voice communication services.
Recently, as the next generation mobile communication system of the 3rd Generation Partnership Project (3GPP), a Long Term Evolution (LTE) system is has been developed. The LTE system is a technology for implementing high-speed packet-based communication at about 100 Mbps that has been available commercially around 2010. Regarding commercialization of the LTE system, a discussion is being held on several schemes such as, one scheme for reducing the number of nodes located in a communication path by simplifying a configuration of a network, and another scheme for maximally approximating wireless protocols to wireless channels.
Unlike voice service, data service is characterized in that a resource is allocated according to the data amount to be transmitted and channel condition. Accordingly, in the wireless communication system such as a cellular communication system, a scheduler manages resource allocation in consideration of the resource amount, channel condition, and data amount. This is also the case in the LTE system as one of the next generation mobile communication systems such that the scheduler located in the base station manages and allocates a radio resource.
Recently, a LTE-Advanced (LTE-A) system has been actively discussed as an evolution of the LTE system with new techniques to increase a data rate. Carrier Aggregation (CA) is one technique that has been newly adopted in the LTE-A system. Unlike data communication according to the related art in which a User Equipment (UE) uses a single uplink carrier and a single downlink carrier, the CA enables the UE to use multiple uplink and/or downlink carriers. Since an uplink transmission power determination algorithm according to the related art is designed for the UE operating with one uplink carrier and one downlink carrier, it is difficult to apply a transmission power determination process according to the related art for uplink transmission power determination of the UE supporting the CA. More particularly, there is a need for a procedure and method for reporting Power Headroom (PH) of the UE supporting the CA.